This invention relates generally to the art of rotogravure printing and in particular to the preparation of a parting solution.
One procedure used in the rotogravure industry for preparing printing cylinders comprises providing a base cylinder which is undersized by approximately 0.006 inches. The base cylinder is cleaned and degreased and is then immersed into a copper plating bath. The negative terminal of a power supply is connected to the base cylinder and positive leads from the power supply are connected to suitable electrodes in the copper plating bath. A voltage is then applied to cause a thin copper coating to be formed on the base cylinder, which coating is then engraved for the printing operation. The details of the plating and printing processes are not provided because such processes are well known to the art.
Because the base cylinders are quite expensive, it is necessary to remove the electro-deposited copper before preparing new printing cylinders. In the past this has usually been accomplished by placing the used cylinder in a lathe and turning the cylinder down to its original size. Such an operation is both time consuming and expensive, and great care is required to control cylinder dimensions with desired limits.
Recently, it has been discovered that the base cylinder can be treated prior to the electro-deposition step to yield a final cylinder which has improved properties. For example, various solutions of mercuric and silver salts can be applied to a cleaned and degreased base copper cylinder by pouring the solution over the cylinder or swabbing the solution on the cylinder with an applicator pad. This solution is known to the art as a "parting solution". The parting solution is rinsed from the cylinder with water and the cylinder is then plated in a conventional manner. The improvement results from the easy removability of the electro-deposited copper shell, which, instead of being turned down with a lathe, can be merely stripped off.
While such parting solutions have become quite popular in the industry from the both a cost and quality control standpoint, they do suffer from several disadvantages including toxicity and pollutant problems. Such prior art parting solutions are, in fact, so highly toxic that their continued use may be prohibited by regulartory agencies of both federal and state governments. It would be highly desirable, therefore, to have a parting solution of equal effectiveness which does not suffer from these drawbacks.